1. Field of the Invention
The present invention relates to a thread breakage detection device for sewing machines, and more specifically to a thread breakage detection device including a permanent magnet member and a hole element provided to a stitch balancing thread tension having a rotary disk.
2. Related Art
There have been provided sewing machines for industrial use capable of stitching multicolor embroidery patterns. One type of such sewing machines includes a needle-bar casing that houses a plurality of needle bars each mounting a needle at its lower end. During embroidery operation, the needle-bar casing is moved right and left to select one of the needles to use. A plurality of thread spools for supplying needle threads are provided on a thread spool stand that is fixed behind the needle-bar casing. A frame, to which a plurality of thread breakage detection sensors and a plurality of stitch balancing thread tensions are attached, is formed to an upper part of the needle-bar casing. The needle threads from the thread spools are supplied to the corresponding needles via the corresponding thread breakage detection sensors and stitch balancing thread tensions.
Each thread breakage detection sensor includes, for example, a shaft that rotates in association with the supply of the needle thread, a photo-interrupter supported on the frame, and an encode disk formed with a plurality of slots. The encode disk is fixed to and integrally rotatable with the shaft, and detects thread breakage based on detection signals from the photo-interrupter.
However, the above conventional configuration requires an increased number of components because of the thread breakage detection sensor provided to the frame, whereby the manufacturing costs of the sewing machine are increased, and the overall configuration becomes complex. This problem is particularly striking in a multi-needle sewing machine for industrial use where a plurality of needles are provided since in this case a plurality of thread breakage detection sensors are required. Also, dust raised during embroidery operation often causes detection error.
It is an object of the present invention to overcome the above problems, and also to provide a thread breakage detection device that can be used in a sewing machine without increasing the number of components, the manufacturing costs, or the size of the sewing machine.
In order to achieve the above and other objects, there is provided a thread breakage detection device used in a stitch balancing thread tension having a shaft and a rotary disk having a surface extending perpendicular to an axial direction of the shaft and rotating in accordance with a supply of a thread. The thread breakage detection device including a permanent magnet member attached to the surface of the rotary disk and generating a magnetic field, a hole element that detects the magnetic field generated in the permanent magnet member and outputs a detection signal based on the detected magnetic field, and a detection unit that detects a thread breakage of the thread based on the detection signal.
There is also provided a stitch balancing thread tension including a stationary member, a shaft relatively rotatable with respect to the stationary member, a rotary disk that applies a tension to a thread, the rotary disk being mounted on the shaft and having a surface that extends perpendicular to an axial direction of the shaft, a permanent magnet member attached to the surface of the rotary disk, and a hole element mounted on the stationary member, the hole element detecting a magnetic field generated in the permanent magnet member.
Further, there is provided a sewing machine including a stationary member, a shaft, a rotary disk, a permanent magnet member, a hole element, a measuring unit, a counting unit, and a detector. The shaft is relatively rotatable with respect to the stationary member. The rotary disk applies a tension to a thread. The rotary disk is mounted on the shaft and has a surface that extends perpendicular to an axial direction of the shaft. The permanent magnet member is attached to the surface of the rotary disk. The hole element mounted on the stationary member, detects a magnetic field generated in the permanent magnet member, and outputs a detection signal based on the detected magnetic field. The measuring unit measures a time duration during an embroidery operation. The counting unit counts a number of times the detection signal changes. The detector detects a thread breakage of the thread when the counting unit does not count a predetermined number within a predetermined time duration during the embroidery operation.